Johannes Kepler

Kepler was born in Weil der Stadt in 1571 and trained for the Lutheran ministry before mathematics claimed him. He became an assistant to the astronomer Tycho Brahe, whose meticulous observations of Mars he inherited and spent years trying to fit.

He abandoned the circle for the ellipse, and from that concession came three laws: planets move in ellipses with the Sun at one focus; they sweep equal areas in equal times; and the square of a planet's period is proportional to the cube of its distance from the Sun. Astronomia nova and Harmonices mundi set out the work.

He also cast horoscopes, wrote a speculative voyage to the Moon, and defended his mother against a charge of witchcraft. He died in Regensburg in 1630 while traveling to collect a debt.

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